Manufacture of cellulose esters: recycle of caustic and/or acid from pre-treatment of pulp

Abstract

A process for the manufacture of cellulose esters is described. The process includes the steps of: pre-treating pulp for the removal of impurities with either caustic or acid or both, esterifying the pre-treated pulp, and recycling the caustic or acid or both from the pre-treating step.

1 . In a process for the manufacture of cellulose esters wherein the process comprising the steps of pre-treating pulp for the removal of impurities with either caustic or acid or both and esterifying the pretreated pulp, the improvement comprising the steps of: 
 recycling the caustic or acid or both from a stream from the pre-treating step.    
   
   
       2 . The process of  claim 1  wherein recycling caustic further comprising: 
 filtering the caustic stream from the pre-treating step; and    recovering caustic to form a filter concentrate.    
   
   
       3 . The process of  claim 1  wherein recycling further comprises the steps of: 
 filtering impurities from the caustic stream from the pre-treating step, and    forming a filtrate for return to the pre-treating of pulp and a concentrate.    
   
   
       4 . The process of  claim 3  wherein filtering comprises the step of: 
 nano-filtering impurities from the caustic stream.    
   
   
       5 . The process of  claim 3  wherein filtering comprises the steps of: 
 pre-filtering particles having a predetermined size from the caustic stream,    nano-filtering impurities from the pre-filtered caustic stream, and    returning the filtrate from the nano-filtering to pre-treating the pulp.    
   
   
       6 . The process of  claim 5  wherein the predetermined size being selected from the group consisting of a particle size of >5 microns.  
   
   
       7 . The process of  claim 3  further comprising the step of: 
 precipitating impurities from the concentrate with a precipitating agent and forming precipitated impurities and a mixture of precipitating agent and caustic.    
   
   
       8 . The process of  claim 7  wherein the precipitating agent being selected from the group consisting of alcohol, ketone, and mixtures thereof.  
   
   
       9 . The process of  claim 8  wherein the alcohol being selected from the group consisting of alcohols containing 1 to 4 carbons.  
   
   
       10 . The process of  claim 8  wherein the ketone being acetone.  
   
   
       11 . The process of  claim 7  further comprising the step of: 
 separating precipitated impurities from the mixture of precipitating agent and caustic.    
   
   
       12 . The process of  claim 7  further comprising the step of: 
 separating the precipitating agent from the mixture of precipitating agent and caustic and forming a precipitating agent stream and a caustic stream.    
   
   
       13 . The process of  claim 12  wherein separating being distilling.  
   
   
       14 . The process of  claim 12  further comprising the step of:. 
 removing impurities from the caustic stream prior to returning the caustic to the pre-treating of the pulp.    
   
   
       15 . The process of  claim 14  wherein removing being selected from the group consisting of extracting and adsorbing.  
   
   
       16 . The process of  claim 1  wherein recycling further comprising the steps of: 
 distilling the acid from the pre-treating step.    
   
   
       17 . The process of  claim 1  wherein recycling further comprising the steps of: 
 filtering the acid from the pre-treating step and forming a filtrate stream and a concentrate stream;    separating acid from the filtrate stream; and    separating acid from the concentrate stream.    
   
   
       18 . The process of  claim 1  wherein recycling further comprises the steps of: 
 filtering impurities from the acid stream from the pre-treating step, and    forming a filtrate and a concentrate.    
   
   
       19 . The process of  claim 18  wherein filtering comprises the step of: 
 nano-filtering impurities from the acid stream.    
   
   
       20 . The process of  claim 18  wherein filtering comprises the steps of: 
 pre-filtering particles having a predetermined size from the acid stream, and    nano-filtering impurities from the pre-filtered acid.    
   
   
       21 . The process of  claim 20  wherein the predetermined size being selected from the group consisting of a particle size of >5 microns.  
   
   
       22 . The process of  claim 18  wherein recycling further comprises extracting acid from the filtrate.  
   
   
       23 . The process of  claim 22  wherein extracting further comprising contacting the acid stream with a solvent.  
   
   
       24 . The process of  claim 23  wherein the solvent being selected from the group consisting of benzene, diethyl ether, diisobutyl ketone, ethyl acetate, methyl amyl ketone, methyl ethyl ketone, methyl t-butyl ether (MTBE), C-6 hydrocarbons, isopropyl acetate, isobutyl acetate, isopropyl ether, and mixtures thereof.  
   
   
       25 . The process of  claim 23  further comprising separating acid from an acid/solvent stream.  
   
   
       26 . The process of  claim 18  wherein recycling further comprises extracting acid from the concentrate.  
   
   
       27 . The process of  claim 26  wherein extracting further comprising contacting the acid stream with a solvent.  
   
   
       28 . The process of  claim 27  wherein the solvent being selected from the group consisting of hexane, pentane, heptane, and mixtures thereof.  
   
   
       29 . The process of  claim 16  further comprising the step of removing any residual impurities.  
   
   
       30 . The process of  claim 29  wherein said impurities being organic solvent extractives.